1. Field of the Invention
This invention relates generally to signals used in railway systems, and more particularly to methods and apparatus for illuminating such signal units.
2. Description of the Related Art
Cantilever crossing signals, such as can be seen in prior art FIG. 1, are currently used in the railroad industry for providing overhead signalling in order to warn motorists of an oncoming train. The cantilever signal structure extends over the road and provides maximum visibility to the motorists. These cantilever signal structures typically have a single upright mast and an elongated arm assembly supported at and extending outward from an upper end of the mast. It is industry practice to secure the cantilever arm assembly to the mast through the use of clamps welded to the arm assembly.
Signal units are then provided along the arm assemblies and sometimes along the mast itself. Signal units contain a light source, typically incandescent lamps, to produce the light signal. External circuitry enables flashes of light to be produced by the lamps. A reflector is then provided adjacent to respective lamps of the signal. Electrical wiring is run along the cantilever signal structure to connect the lamps to a power source located at some distance from the cantilever signal structure.
The mast is typically provided with a ladder so that a signal maintainer may vertically ascend the mast to access the arm assembly. A walkway is provided along the full length of the cantilever arm assembly. The arm assembly walkway allows a maintainer to traverse the length of the arm assembly to service and maintain the signal units attached to the arm assembly, such as to replace the lamps of the signal units. The ladder and walkway are used instead of a separate platform, truck or train so that the signals may be serviced and maintained without impeding traffic.
It is standard industry practice to run electrical wiring up through the signal masts and out along the horizontal structure to the particular signal units along the assembly. If a signal unit malfunctions or if a signal unit lamp requires replacement, a maintainer must climb the mast ladder and traverse the arm assembly walkway to that signal unit. Traversing the ladder and walkway add additional time to the replacement process. Furthermore, as the length of electrical wiring increases, the likelihood that a short somewhere along that electrical wiring also increases.
In some respects, the use of an overhead mast ladder and an arm assembly walkway may be undesirable. For example, there are always risks associated with a maintainer scaling an elevated structure especially in adverse weather conditions. A chain may typically be provided at the end of the walkway and handrails are provided on either side of the walkway to prevent a maintainer from falling from the arm assembly walkway. Furthermore, the maintainer may have to attach a safety belt to reduce the risk associated with the height of the walkway. In order to prevent unauthorized individuals from ascending the cantilever signal, anticlimb guards have been designed in the railroad signalling industry which may be affixed to the mast ladder. Unfortunately, such anticlimb guards could potentially circumvented. Furthermore, rain and snow may accumulate on the arm assembly walkway, which could cause the increased hazard of ice during adverse weather conditions.
Thus, it would be advantageous to develop an overhead signal structure that did not require a maintainer to scale a ladder and traverse an overhead walkway for routine maintenance.